Whilst its all great being able to buy cosmetic sets for your ships, how great would it be if you could find Rare [ ;) ] stuff like a ship wheel buried at the bottom of a hidden cave from a sunken legendary ship. There could be notebooks around that detail legendary vessels, both expanding on lore and providing some more unique cosmetics.
Now it could be a quest system from the notebooks that lead you around the map but personally Id prefer just a single element of rng. All we know is these ships have eventually sunk and out in the world is parts of them (sails, wheel, a cannon, art schematics for hull design as a hull would be pretty obvious haha). So you could be doing abit of spelunking and stumble across a sunken cannon, you could be digging up a chest on a beach and see part of a wheel poking out of the sand near a palm tree or a part of a sail has wrapped itself around a tall peak of an island. Think throne hunting in terms of locations.
They wouldnt immediately be available for use, they would need repairing, afterall theyve come off a sunken ship to be salvaged by yourself. Thus it would need some ridiculout amount of wood and other materials until its available for use e.g sails are going to require a whole bunch of fabric...guess some of those merchant crates wont be getting delivered. Wheels are going to need some wood, best get 200 pieces and 10 bananas (its hungry work afterall). Found a design for a hull? Lucky you! but youre gonna need a forest and a big ol' chest of gold for the shipwright to put it together for you.
Ending result, encourages some exploration and ultimately some rare cosmetics that not everyone will have just because theyve got a tonne of gold.